Showing papers by "Nika Akopian published in 2016"
TL;DR: It is shown for the first time that crystal phase quantum dots are a source of pure single-photons and cascaded photon-pairs from type II transitions with excellent optical properties in terms of intensity and line width.
Abstract: We report the first comprehensive experimental and theoretical study of the optical properties of single crystal phase quantum dots in InP nanowires. Crystal phase quantum dots are defined by a transition in the crystallographic lattice between zinc blende and wurtzite segments and therefore offer unprecedented potential to be controlled with atomic layer accuracy without random alloying. We show for the first time that crystal phase quantum dots are a source of pure single-photons and cascaded photon-pairs from type II transitions with excellent optical properties in terms of intensity and line width. We notice that the emission spectra consist often of two peaks close in energy, which we explain with a comprehensive theory showing that the symmetry of the system plays a crucial role for the hole levels forming hybridized orbitals. Our results state that crystal phase quantum dots have promising quantum optical properties for single photon application and quantum optics.
44 citations
TL;DR: In this paper, the origin of spontaneous core-shell AlGaAs nanowires grown by gold-assisted molecular beam epitaxy was unraveled based on high-angle annular dark-field scanning transmission electron microscopy and energy dispersive X-ray spectroscopy studies.
Abstract: Based on the high-angle annular dark-field scanning transmission electron microscopy and energy dispersive X-ray spectroscopy studies, we unravel the origin of spontaneous core–shell AlGaAs nanowires grown by gold-assisted molecular beam epitaxy. Our AlGaAs nanowires have a cylindrical core and a tapered shell. The composition of the shell is close to nominal, while the aluminum content in the core is systematically smaller than nominal. After switching off the group III fluxes, the aluminum content in the droplet and in the topmost part of the nanowire rapidly tends to zero, while gallium remains there at a high percentage. We present a quantitative model to explain these findings. Lower aluminum composition in the core is attributed to its lower surface diffusivity, with the aluminum collection length of 250 nm against 780 nm for gallium at the substrate temperature 510 °C and under the nominal aluminum content of 0.2. These values decrease to 8 and 160 nm when the nominal aluminum content is raised to ...
38 citations